STANFORD — The immediate surroundings — the trenches — will be intensely familiar to Brennan Scarlett: Current Stanford teammates lined up next to him, former Cal teammates on the other side of the line of scrimmage.

But the environment Saturday will be novel for the first player in the modern era to play football for both schools.

Scarlett arrived in Berkeley in the summer of 2011 and started four seasons with the Bears. Because of injuries, he finished none of them.

This will be his first Big Game.

“It’s definitely going to be an interesting day,” Scarlett said. “It’s personal, but that’s not going to change the way I play and prepare.”

Scarlett played his finest game in a Cardinal uniform last week against Oregon (2.5 sacks and a forced fumble) and has been critical to the rebuilt defense all season. Without him, a worrisome situation on the line would have turned dire when nose tackle Harrison Phillips was lost to a season-ending injury in September.

“He’s enabled us to play our defense, because we were so short on linemen,” defensive coordinator Lance Anderson said. “Frankly, I don’t know what we would have done without him.”

Scarlett’s presence adds a dynamic to the 118th Big Game that would seem to favor the Cardinal.

He can provide Stanford’s defensive staff with insights into how to attack Cal’s offense, particularly up front: He faced the Bears offensive linemen each day in practice.

Stanford coach David Shaw said he would not ask Scarlett for any information about the Bears. “I don’t believe in that,” he said. Whether Scarlett whispers suggestions to the assistant coaches and his linemates is another matter.

Cal coach Sonny Dykes isn’t concerned.

“Not at all,” he said. “We change the stuff enough, I don’t think it’s an issue.”

Scarlett made the move across the Bay in the spring in order to play with his brother Cameron, a Stanford freshman, and pursue his graduate studies in management science and engineering — a degree that Cal doesn’t offer.

He has frequently mentioned having good friends on the Cal roster and communicating with them regularly. His view of lining up against the Bears — fun, wholesome competition — seems to mirror the approach Cal’s offensive linemen are talking.

“I have nothing against him,” guard Jordan Rigsbee said. “We’re still good buddies. I’ll say hi to him, all that stuff. When it comes down to (playing), he’ll be like anyone else.”

Scarlett’s feelings for the Cal staff aren’t as clear. He has made reference to “awkward conversations” during the transfer process and was taken aback by Dykes’ terse reaction.

“Gone,” said Dykes, who later added: “Don’t care.”

The next day, athletic director Michael Williams released a statement that noted Scarlett’s “tremendous character” and said the school would not block his request to transfer.

Asked last week if he had any hard feelings, Dykes said: “You don’t ever want to lose players, but that’s part of the deal.”

But there has never been a deal like Scarlett’s.

At the time the transfer to Stanford went public, he was still a Cal student recovering from Cal football injuries and in need of Cal medical treatment — an unprecedented, awkward and potentially emotional situation.

The Bears determined that it would be in the best interest of all involved if Scarlett didn’t rehabilitate alongside his suddenly ex-teammates. He used the Haas Pavilion facilities with all other Cal athletes, rather than the football program’s home at the Simpson Center.

“No hostility,” Scarlett said. ‘That’s just how it shook out.”

Scarlett joined Stanford in the summer and immersed himself in the playbook and offseason conditioning, with an emphasis on flexibility.

Over time, his strength and quickness have improved, his knowledge of the playbook has deepened, and he has grown more comfortable with Stanford’s system. He is tied for the team lead in quarterback hurries and is second in sacks.

“He’s made as many plays coming at him as going away from him, running down the backside,” Shaw said. “Those are the plays Trent Murphy made, the plays Chase Thomas made, the plays Shayne Skov made. He’s doing everything he can every week.